The invention relates to a process for obtaining gaseous oxygen at elevated pressure by way of low temperature rectification of air, in which the air is compressed, purified, and at least in part, is cooled in a first heat exchanger in heat exchange with rectification product and is passed to the rectication, while a second gas stream is compressed to elevated pressure, is cooled in a second heat exchanger in heat exchange with rectification product, is expanded and likewise is passed into the rectification, and in which process, liquid oxygen is removed from the rectification, pumped to the desired pressure and then is evaporated and heated in heat exchange with the compressed gas stream, which is at elevated pressure; the invention also relates to a device for carrying out the process.
Such process is known from German Laid Open Patent Application No. 25 57 453. Liquid oxygen is removed from the rectification, is compressed to the desired elevated pressure and subsequently is evaporated and heated. Elevated pressure is meant to be superatmospheric pressure here. The heat required for evaporation and heating of the oxygen is supplied by a compressed stream of air. Due to their different physical properties, the temperature curves of oxygen and air differ in the heat exchange. The resultant relatively large temperature differences at the cold end of the second heat exchanger translate into a loss of energy.
This process, which is known as "internal compression" (Innenverdichtung) for the production of oxygen gas under pressure, is thus relatively costly in terms of energy. It has the advantage, however, that the compression of liquid oxygen can be effected with a greatly reduced risk of fire when compared to the more energy efficient process with "external compression" (Aussenverdichtung) of the oxygen, in which the oxygen is withdrawn in gaseous form, essentially without pressure, from the rectification and is then heated and compressed to the required output pressure.
It is the objective of the invention to provide a process of the kind initially described, in which the energy requirements for the production of oxygen are reduced.
The inventive process achieves this objective in that a third partial gas stream to be fractionated is cooled in heat exchange with product to be fractionated.